Session 21: Distortion, Grunge, and Output Hack

Objective: Use distortion, grunge, and output hack to add aggression, lo-fi character, and timbral destruction to your sounds, understanding pre/post signal positioning.

Warm-Up (2 min)

Load your plucked string patch from Session 20. Play a few notes across the keyboard to hear the Karplus-Strong synthesis. That was feedback as a sound generator. Today you will use distortion and bit-crushing as timbral shapers -- the Evolver's destructive effects. Load the basic patch.

Setup

From the basic patch:

• Set Osc 1 Level to 40, Osc 2 Level to 40
• Set Osc 3 Level to 0, Osc 4 Level to 0
• Set LPF Frequency to 100, Resonance to 20, 4-Pole ON
• Set ENV 1 (Filter): Decay = 70, Sustain = 30, Env Amount = 50
• Set ENV 2 (VCA): Attack = 0, Decay = 0, Sustain = 100, Release = 20
• Lower Main Volume before starting -- distortion dramatically increases loudness

This gives a mildly filtered sound with some envelope movement as a canvas for destructive effects.

Exercises

Exercise 1: Distortion Basics (5 min)

Distortion is digital clipping that squares off waveform peaks, adding harmonics and aggression (Anu Kirk p.54-55). It ranges from 0-99.

1. Set Distortion to 15 -- play a note. You should hear a subtle edge added to the sound, like mild overdrive
2. Increase to 40 -- more obvious distortion, the tone becomes more aggressive and harmonically rich
3. Increase to 75 -- heavy distortion. The waveform is being severely clipped. Notice how the volume has increased dramatically
4. Set Distortion to 99 -- maximum. The sound is very compressed and aggressive
5. Try playing at different pitches -- distortion sounds different on low notes vs high notes because it emphasizes higher harmonics
6. Set Distortion back to 40. Now sweep LPF Frequency from 100 down to 40 -- the filter tames the harshness of the distortion. This is a key technique: distort then filter (Anu Kirk p.54)

Important: Whenever distortion is non-zero, the Evolver's noise gate activates. The noise gate is triggered by the left channel level (DSI Manual p.19). If you want the noise gate alone without distortion, set Distortion to 1.

Exercise 2: Pre/Post Distortion Positioning (4 min)

Distortion can be placed at two points in the signal chain. This changes its character dramatically (DSI Manual p.26).

1. Keep Distortion at 40
2. Open Misc Params and find Dist Pre/Post. Set to Post (After VCA) -- this is the default for internal sounds. Distortion comes after the filter and VCA
3. Play notes and listen -- the distortion affects the fully shaped sound
4. Switch to Pre (After ExtIn) -- now distortion is placed before the analog filter. For internal oscillators, this positioning only affects external input. You should hear the distortion disappear or change character on internal sounds
5. Switch back to Post (After VCA) for the rest of this session

Key insight: Post = distortion on everything (internal sounds). Pre = distortion on external input only, allowing the analog filter to shape the distorted signal.

Exercise 3: Output Hack -- Bit Crushing (4 min)

Output Hack reduces bit depth from 16 bits down to 2 bits. It "trashes the output signal, quite rudely" (DSI Manual p.21).

1. Set Distortion to 0 (isolate the output hack effect)
2. Set Output Hack to 4 -- play a note. You should hear a subtle gritty texture added
3. Increase to 8 -- the sound becomes noticeably lo-fi, like an old video game console
4. Increase to 12 -- extreme bit crushing. The sound is heavily degraded, stairstepped, and crunchy
5. Set to 14 -- only 2 bits remain. The sound is almost pure square wave at any input
6. Now combine: set Distortion to 30 and Output Hack to 6 together -- distortion adds harmonics, then output hack crushes the resolution. The combination is more extreme than either alone

Exercise 4: Grunge and the Dirty Lead (5 min)

Grunge intensifies the feedback character (Anu Kirk p.56). Combined with distortion, it creates aggressive leads.

1. Set Output Hack to 0, Distortion to 45
2. Set Feedback Level to 50, Feedback Frequency to 24 (C2)
3. Turn Grunge ON
4. Play notes -- you should hear a harsh, aggressive quality layered on top of your sound from the feedback interacting with the distortion and grunge circuit
5. Increase Feedback Level to 70 -- the grunge character becomes more prominent. At higher feedback levels, grunge "enables nasty feedback" (DSI Manual p.19)
6. Add some filter envelope: set Env Amount to 65 -- the filter sweep through the distortion creates a classic dirty synth lead sound
7. Set Osc Slop to 3 for some analog drift, and Osc 2 Fine to +5 for detuning thickness

Save this patch as your "Dirty Lead" patch.

Exploration (optional, hyperfocus days)

• Combine all three: Distortion = 50, Output Hack = 5, Grunge = ON, Feedback Level = 60. Extreme destruction
• Add your rhythmic delay from Session 19 (Delay 1 Time = 1 Step, Level = 50, Feedback 1 = 40) to the dirty lead -- distorted delay is a classic sound
• Try HP Pre/Post switching in Misc Params -- moving the highpass filter changes which frequencies reach the distortion

Output Checklist

• Dirty lead patch saved with distortion, grunge, and feedback
• Understand distortion (0-99), output hack (0-14 bit reduction), and grunge (feedback intensifier)
• Heard the difference between pre/post distortion positioning
• Session logged in Obsidian daily note

Key Takeaways

• Distortion clips waveforms, adding harmonics and aggression; output hack reduces bit depth for lo-fi character; grunge intensifies feedback harshness
• Pre/post positioning changes what gets distorted: Post affects everything, Pre affects only external input (allowing the analog filter to tame it)
• The noise gate activates whenever distortion is non-zero -- use distortion = 1 for noise gate only without audible distortion

Next Session Preview

Session 22 introduces the Evolver's 4-track, 16-step sequencer -- the instrument's killer feature. You will program basic sequences, understand step values, and create your first sequenced melody.